Luminescent element

ABSTRACT

A light-emitting element is disclosed, which comprises a substrate having provided thereon a pair of opposed electrodes between which are provided a light-emitting layer containing at least one light-emitting material selected from the compounds represented by the following general formula (I) and a host material, and which has an organic membrane having a larger ionization potential than that of the host material between the light-emitting layer and the cathode, with the organic membrane being in contact with the light-emitting layer: general formula (I)  
                 
 
     wherein R 1 , R 2 , R 3 , R 4  and R 5  may be the same or different from each other and each represents a hydrogen atom or a substituent, X represents an oxygen atom, a sulfur atom or N-R Y1 , R Y1  represents a hydrogen atom or a substituent, L represents a linking group comprising a conjugated bond, R X  and R Y  may be the same or different from each other and each represents a hydrogen atom or a substituent, with at least one of them being an electron-withdrawing group.  
     The light-emitting element of the invention has a small temperature dependence of response upon pulse driving, and is excellent in red purity, light-emitting efficiency and durabiloity.

TECHNICAL FIELD

[0001] The present invention relates to a light-emitting element whichcan be utilized in the field of back light, flat panel display, lightsources for illumination, display elements, electrophotography, organicsemiconductor lasers, recording light sources, reading light sources,signs, signboards, and optical communication devices.

BACKGROUND ART

[0002] In these days, research and development on various light-emittingelements have been vigorously conducted. Of them, organicelectroluminescent (EL) elements have attracted attention as promisinglight-emitting elements due to their advantages of ultra-thin thicknessand light weight, high response speed, wide viewing angle, and lowdriving voltage. In general, the organic EL elements comprise alight-emitting layer sandwiched by a pair of opposed electrodes andutilize a light emitted from excitons generated by recombination of anelectron injected from a cathode and a hole injected from an anode.

[0003] Presently known organic EL elements capable of giving a highlybright luminance at a low voltage are those which are disclosed by Tangand which have a layered structure (Applied Physics Letters, vol.51,p.913, 1987). These elements have an electron-transporting andlight-emitting material and a hole transporting material in a layeredform which serves to emit a high-luminance green light, and they give aluminance as high as several thousands cd/m² at a direct current voltageof 6 to 7 V. However, in consideration of their use as a full colordisplay or a light source, emission of lights of three primary colors ora white light is practically necessary. The above-described elements usea 8-quinolinol aluminum complex as a light-emitting material, and thecolor of the light emitted therefrom is limited to green. Hence,light-emitting elements capable of emitting a light of other color havebeen desired to be developed. As materials capable of emitting a lightof a longer wavelength than green, there have so far been developed suchlight-emitting materials as4-(dicyanomethylene)-2-methyl-(4-dimethylaminostyryl)-4H-pyran (DCM) andits derivatives, Nile Red derivatives and Eu (III) complexes. However,they have the defects of, for example, poor color purity, low luminanceof an emitted light, low light-emitting efficiency, and low durability.

[0004] Thus, various investigations have been made. Elements usingcompounds having a cyclic acidic nucleus such as those compounds whichare described in JP-A-11-335661 were prepared and evaluated and werefound to be excellent in red color purity, emitted light luminance,light-emitting efficiency and durability.

[0005] However, in the case of preparing an element wherein one and thesame compound is used as the electron injecting and transporting layeron the cathode side and a host material in the light-emitting layer aswith the vacuum deposition type element described in the Example, thereresult a poor luminance response and a large temperature dependence ofthe pulse width of an emitted light in pulse driving. Therefore, in thecase of applying them to light sources for exposure, they are notadapted for creating a wide gradation by pulse modulation. Thus,improvement of response properties upon pulse driving, particularlytemperature dependence of the pulse width of an emitted light, have beendesired. Also, light-emitting efficiency has been desired to be moreimproved.

DISCLOSURE OF THE INVENTION

[0006] An object of the invention is to provide a light-emitting elementwhich has improved response properties upon pulse driving, particularlyshows a small temperature dependence of the pulse width of an emittedlight.

[0007] Another object of the invention is to provide a light-emittingelement which is excellent in red color purity, light-emittingefficiency and durability.

[0008] The above-described objects of the invention are attained by thefollowing.

[0009] 1. A light-emitting element, which comprises a substrate havingprovided thereon a pair of opposed electrodes between which are provideda light-emitting layer containing at least one light-emitting materialselected from the compounds represented by the following general formula(I) and a host material, and which has an organic membrane having alarger ionization potential than that of the host material between thelight-emitting layer and the cathode, with the organic membrane being incontact with the light-emitting layer: general formula (I)

[0010] wherein R¹, R², R³, R⁴ and R⁵ may be the same or different fromeach other and each represents a hydrogen atom or a substituent, Xrepresents an oxygen atom, a sulfur atom or N-R^(Y1), R^(Y1) representsa hydrogen atom or a substituent, L represents a linking groupcomprising a conjugated bond, R^(X) and R^(Y) may be the same ordifferent from each other and each represents a hydrogen atom or asubstituent, with at least one of them being an electron-withdrawinggroup.

[0011] 2. The light-emitting element as described in 1, wherein thedifference in ionization potential between the organic membrane and thehost material in the light-emitting layer is 0.01 eV to 2 eV.

[0012] 3. The light-emitting element as described in 1 or 2, wherein theionization potential of the organic membrane is more than 5.7 eV and notmore than 7.0 eV.

[0013] 4. The light-emitting element as described in one of 1 to 3,wherein the organic membrane comprises at least one compound selectedfrom among the compounds represented by the general formulae (V) to(XI):

[0014] wherein, in the general formula (V), R⁵⁵ and R⁵⁶ may be the sameor different from each other and each represents an alkyl group, an arylgroup or a hetero ring group, X represents an oxygen atom, a sulfur atomor N-R^(Y5), and R^(Y5) represents a hydrogen atom or a substituent and,in the general formula (VI), A represents a hetero ring group containingtwo or more hetero atoms, with the hetero ring groups represented by Abeing optionally the same or different from each other, m⁶ represents aninteger of 2 or more, and L⁶ represents a linking group and, in thegeneral formula (VII), R⁷¹ represents a substituent, R⁷² represents ahydrogen atom, an aliphatic group, an aryl group or an aromatic heteroring group, M represents a metal atom, n⁷ represents an integer of 0 to6 and m⁷ represents 2 or 3, with the proviso that, when m⁷=3, then n⁷≠0and, in the general formula (VIII), X⁸¹ represents a nitrogen atom orC—R⁸¹, X⁸² represents an oxygen atom, a sulfur atom or N—R^(Y8), R⁸¹,R⁸², R⁸³ and R^(Y8) may be the same or different from each other andeach represents a hydrogen atom or a substituent, with R⁸¹ and R⁸² beingoptionally connected to each other to form a ring, R⁸⁴ represents ahydrogen atom, an alkyl group, an aryl group or an aromatic hetero ringgroup, M represents a metal atom, one represents an integer of 0 to 4,and me represents 2 or 3 and, in the general formula (IX), R⁹¹represents a substituent, with a plurality of R⁹¹ s optionally beingconnected to each other to form a fused ring, R⁹² to R⁹⁴ may be the sameor different from each other and each represents a hydrogen atom or asubstituent, and m⁹ represents an integer of 0 to 5 and, in the generalformula (X), R¹⁰¹ and R¹⁰² may be the same or different from each otherand each represents a hydrogen atom or a substituent, R¹⁰³ to R¹⁰⁶ maybe the same or different from each other and each represents asubstituent, L¹⁰ represents a linking group, and m¹⁰, n¹⁰, p10 and q¹⁰may be the same or different from each other and each represents aninteger of 0 to 5 and, in the general formula (XI), Ar¹¹¹ represents atrivalent arylene group, Ar¹¹² to Ar¹¹⁴ may be the same or differentfrom each other and each represents an aryl group.

[0015] 5. The light-emitting element as described in one of 1 to 4,wherein the compound represented by the general formula (I) is acompound represented by the following general formula (II):

[0016] wherein R¹, R², R³, R⁴ and R⁵ may be the same or different fromeach other and each represents a hydrogen atom or a substituent, Xrepresents an oxygen atom, a sulfur atom or N—R^(Y1), R^(Y1) representsa hydrogen atom or a substituent, Z represents atoms necessary forforming 5- or 6-membered ring, L₂₁ and L₂₂ may be the same or differentfrom each other and each represents a methine group, a substitutedmethine group or a nitrogen atom, n represents an integer of 0 to 3, andAr represents an arylene group or a divalent aromatic hetero ring group.

[0017] 6. The light-emitting element as described in 6, wherein thecompound represented by the general formula (II) is a compoundrepresented by the following general formula (III):

[0018] wherein R₁, R², R³, R⁴, R⁵, R³¹, R³², R³³ and R³⁴ may be the sameor different from each other and each represents a hydrogen atom or asubstituent, Z³ represents atoms necessary for forming 5- or 6-memberedring, L₂₁ and L₂₂ may be the same or different from each other and eachrepresents a methine group, a substituted methine group or a nitrogenatom, and n represents an integer of 0 to 3.

[0019] 7. The light-emitting element as described in 6, wherein thecompound represented by the general formula (III) is a compoundrepresented by the following general formula (IV):

[0020] wherein R¹, R², R³, R⁴, R⁵, R³¹, R³², R³³, R³⁴, R⁴¹, R⁴², R⁴³ andR⁴⁴ may be the same or different from each other and each represents ahydrogen atom or a substituent, and R^(A1) and R^(A2) may be the same ordifferent from each other and each represents a hydrogen atom or asubstituent and, when possible, R^(A1) and R^(A2) maybe connected toeach other and further to other substituent to form a ring.

[0021] 8. The light-emitting element as described in one of 1 to 7,wherein the host material is an aluminum quinoline derivative.

[0022] 9. The light-emitting element as described in one of 1 to 8,wherein the content of the at least one compound selected from thecompounds represented by the general formulae (I) to (IV) in thelight-emitting layer is 0.01% by weight to 50% by weight.

[0023] 10. The light-emitting element as described in one of 4 to 9,wherein the content of the at least one compound selected from thecompounds represented by the general formulae (V) to (XI) in the organicmembrane is 50% by weight to 100% by weight.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] The invention is described in detail below.

[0025] The light-emitting element of the invention is an element whereina light-emitting layer or a plurality of organic compound layersincluding the light-emitting layer are formed between two electrodes ofan anode and a cathode. It may have a hole injecting layer, a holetransporting layer, an electron injecting layer, an electrontransporting layer and a protective layer in addition to thelight-emitting layer. These layers may additionally exert functions ofother layers.

[0026] First, the compounds of the invention represented by the generalformula (I) are described below.

[0027] R¹, R², R³, R⁴ and R⁵ may be the same or different from eachother and each represents a hydrogen atom or a substituent.

[0028] Examples of the substituent represented by R¹ to R⁵ include analkyl group (containing preferably 1 to 20, more preferably 1 to 12,particularly preferably 1 to 8, carbon atoms, and being exemplified bymethyl, ethyl, iso-propyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl,cyclopropyl, cyclopentyl and cyclohexyl), an alkenyl group (containingpreferably 2 to 20, more preferably 2 to 12, particularly 2 to 8, carbonatoms, and being exemplified by vinyl, allyl, 2-butenyl and 3-pentenyl),an alkynyl group (containing preferably 2 to 20, more preferably 2 to12, particularly preferably 2 to 8, carbon atoms, and being exemplifiedby propargyl and 3-pentynyl), an aryl group (containing preferably 6 to30, more preferably 6 to 20, particularly preferably 6 to 12, carbonatoms, and being exemplified by phenyl, p-methylphenyl, naphthyl,anthryl, phenanthryl and pyrenyl) , an amino group (containingpreferably 0 to 20, more preferably 0 to 12, particularly preferably 0to 6, carbon atoms, and being exemplified by amino, methylamino,dimethylamino, diethylamino, diphenylamino and dibenzylamino), an alkoxygroup (containing preferably 1 to 20, more preferably 1 to 12,particularly preferably 1 to 8, carbon atoms, and being exemplified bymethoxy, ethoxy and butoxy), an aryloxy group (containing preferably 6to 20, more preferably 6 to 16, particularly preferably 6 to 12, carbonatoms, and being exemplified by phenyloxy and 2-napthyloxy), a heteroring oxy group (containing preferably 2 to 20, more preferably 3 to 16,particularly preferably 4 to 12, carbon atoms, and being exemplified bypyridinoxy pyrimidinoxy, pyridazinoxy and benzimidazolyloxy), a silyloxygroup (containing preferably 3 to 40, more preferably 3 to 30,particularly preferably 3 to 20, carbon atoms, and being exemplified bytrimethylsilyloxy and t-butyldimethyloxy), an acyl group (containingpreferably 1 to 20, more preferably 1 to 16, particularly preferably 1to 12, carbon atoms, and being exemplified by acetyl, benzoyl, formyland pivaloyl), an alkoxycarbonyl group (containing preferably 2 to 20,more preferably 2 to 16, particularly preferably 2 to 12, carbon atoms,and being exemplified by methoxycarbonyl and ethoxycarbonyl), anaryloxycarbonyl group (containing preferably 7 to 20, more preferably 7to 16, particularly preferably 7 to 10, carbon atoms, and beingexemplified by phenyloxycarbonyl), an acyloxy group (containingpreferably 2 to 20, more preferably 2 to 16, particularly preferably 2to 10, carbon atoms, and being exemplified by acetoxy and benxoyloxy),an acylamino group (containing preferably 2 to 20, more preferably 2 to16, particularly preferably 2 to 10, carbon atoms, and being exemplifiedby acetylamino and benzoylamino), an alkoxycarbonylamino group(containing preferably2 to 20, more preferably 2 to 16, particularlypreferably 2 to 12, carbon atoms, and being exemplified bymethoxycarbonylamino), an aryloxycarbonylamino group (containingpreferably 7 to 20, more preferably 7 to 16, particularly preferably 7to 12, carbon atoms, and being exemplified by phenyloxycarbonylamino), asulfonylamino group (containing preferably 1 to 20, more preferably 1 to16, particularly preferably 1 to 12, carbon atoms, and being exemplifiedby methanesulfonylamino and benzenesulfonylamino), a sulfamoyl group(containing preferably 0 to 20, more preferably 0 to 16, particularlypreferably 0 to 12, carbon atoms, and being exemplified by sulfamoyl,methylsulfamoyl, dimethylsulfamoyl and phenylsulfamoyl), a carbamoylgroup (containing preferably 1 to 20, more preferably 1 to 16,particularly preferably 1 to 12, carbon atoms, and being exemplified bycarbamoyl, methylcarbamoyl, diethylcarbamoyl and phenylcarbamoyl), analkylthio group (containing preferably 1 to 20, more preferably 1 to 16,particularly preferably 1 to 12, carbon atoms, and being exemplified bymethylthio and ethylthio), an arylthio group (containing preferably 6 to20, more preferably 6 to 16, particularly preferably 6 to 12, carbonatoms, and being exemplified by phenylthio) , a hetero ring thio group(containing preferably 6 to 20, more preferably 6 to 16, particularlypreferably 6 to 12, carbon atoms, and being exemplified by pyridinothio,pyrimidinothio, pyridazinothio, benzimidazolylthio andthiadiazolylthio), a sulfonyl group (containing preferably 1 to 20, morepreferably 1 to 16, particularly preferably 1 to 12, carbon atoms, andbeing exemplified by mesyl and tosyl), a sulfinyl group (containingpreferably 1 to 20, more preferably 1 to 16, particularly preferably 1to 12, carbon atoms, and being exemplified by methanesulfinyl andbenzenesulfinyl), an ureido group (containing preferably 1 to 20, morepreferably 1 to 16, particularly preferably 1 to 12, carbon atoms, andbeing exemplified by ureido, methylureido and phenylureido), aphosphoric acid amido group diethylphosphoric acid amido andphenylphosphoric acid amido), a hydroxyl group, a mercapto group, ahalogen atom (such as a fluorine atom, a chlorine atom, a bromine atomor an iodine atom), a cyano group, a sulfo group, a carboxyl group, anitro group, a hydroxamic acid group, a sulfino group, a hydrazinegroup, an imino group, a hetero ring group (containing preferably 1 to30, more preferably 1 to 12, carbon atoms and a hetero atom or atomssuch as a nitrogen atom, an oxygen atom and a sulfur atom , and beingexemplified by imidazolyl, pyridyl, quinolyl, furyl, thienyl, piperidyl,morpholino, benzoxazolyl, benzimidazolyl, benzothiazolyl, carbazolyl andazepinyl), and a silyl group (containing preferably 3 to 40, morepreferably 3 to 30, particularly preferably 3 to 24, carbon atoms, andbeing exemplified by trimethylsilyl and triphenylsilyl). Thesesubstituents may further be substituted. Also, in the case where two ormore substituents exist, they may be the same or different from eachother. Also, where possible, they may be connected to each other to forma ring.

[0029] R¹ and R² each preferably represents a hydrogen atom, analiphatic hydrocarbyl group, an aryl group, a hetero ring group or, whenconnected to L through an alkylene group, forms a 5- or 6-membered ringor, when taken together, R¹ and R² preferably form a 5- to 7-memberedring. More preferably, R¹ and R² each represents a hydrogen atom, analkyl group, an aryl group or, when connected to L through an alkylenegroup, forms a 5- or 6-membered ring or, when taken together, R¹ and R²form a 5- to 7-membered ring. Particularly preferably, R¹ and R² eachrepresents a methyl group, an ethyl group or, when connected to Lthrough an alkylene group, forms a 5- or 6-membered ring or, when takentogether, R¹ and R² form a 5- to 7-membered ring.

[0030] R³ preferably represents a hydrogen atom, an aslkyl group, anaryl group, a halogen atom or a cyano group, more preferably, a hydrogenatom or an alkyl group, still more preferably a hydrogen atom.

[0031] R⁴ preferably represents a hydrogen atom, an alkyl group, an arylgroup, an aromatic hetero ring group or, when connected to R⁵, forms aring. More preferably, R⁴ represents a hydrogen atom or an alkyl group,still more preferably a hydrogen atom.

[0032] R⁵ preferably represents a hydrogen atom, an alkyl group, an arylgroup, an aromatic hetero ring group or, when connected to R⁴, forms aring. More preferably, R⁵ represents an alkyl group (preferably an alkylgroup containing 2 to 20 carbon atoms, more preferably a branched orcyclic alkyl group containing 3 to 20 carbon atoms, still morepreferably a branched or cyclic alkyl group containing 4 to 12 carbonatoms and containing a tertiary carbon atom, particularly preferably atert-butyl group) or an aryl group (preferably an aryl group having asubstituent at an o-position, more preferably an alkyl-substitutedphenyl group containing up to 30 carbon atoms and having a substituentat an opposition, still more preferably, a substituted 2,6-dimethylphenyl group, particularly preferably a 2,4,6-trimethylphenyl group),particularly preferably a tert-butyl group, 2,4,6-trimethylphenyl group,most preferably a tert-butyl group.

[0033] X represents an oxygen atom, a sulfur atom or N—R^(Y1), R^(Y1)represents a hydrogen atom or a substituent. Examples of the substituentrepresented by R^(Y1) include an alkyl group (containing preferably 1 to20 carbon atoms, more preferably 1 to 12 carbon atoms, particularlypreferably 1 to 8 carbon atoms and being exemplified by methyl, ethyl,iso-propyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl,cyclopentyl and cyclohexyl), an alkenyl group (containing preferably 2to 20, more preferably 2 to 12, particularly 2 to 8, carbon atoms, andbeing exemplified by vinyl, allyl, 2-butenyl and 3-pentenyl), an alkynylgroup (containing preferably 2 to 20, more preferably 2 to 12,particularly preferably 2 to 8, carbon atoms, and being exemplified bypropargyl and 3-pentynyl) , an aryl group (containing preferably 6 to30, more preferably 6 to 20, particularly preferably 6 to 12, carbonatoms, and being exemplified by phenyl, p-methylphenyl and naphthyl), anacyl group (containing preferably 1 to 20, more preferably 1 to 16,particularly preferably I to 12, carbon atoms, and being exemplified byacetyl, benzoyl, formyl and pivaloyl), an alkoxycarbonyl group(containing preferably 2 to 20, more preferably 2 to 16, particularlypreferably 2 to 12, carbon atoms, and being exemplified bymethoxycarbonyl and ethoxycarbonyl), an aryloxycarbonyl group(containing preferably 7 to 20, more preferably 7 to 16, particularlypreferably 7 to 10, carbon atoms, and being exemplified byphenyloxycarbonyl), a sulfamoyl group (containing preferably 0 to 20,more preferably 0 to 16, particularly preferably 0 to 12, carbon atoms,and being exemplified by sulfamoyl, methylsulfamoyl, dimethylsulfamoyland phenylsulfamoyl), a carbamoyl group (containing preferably 1 to 20,more preferably 1 to 16, particularly preferably 1 to 12, carbon atoms,and being exemplified by carbamoyl, methylcarbamoyl, diethylcarbamoyland phenylcarbamoyl), a sulfonyl group (containing preferably 1 to 20,more preferably 1 to 16, particularly preferably 1 to 12, carbon atoms,and being exemplified by mesyl and tosyl), a sulfinyl group (containingpreferably 1 to 20, more preferably 1 to 16, particularly preferably 1to 12, carbon atoms, and being exemplified by methanesulfinyl andbenzenesulfinyl), and a hetero ring group (containing preferably 1 to20, more preferably 1 to 12, carbon atoms and a hetero atom or atomssuch as a nitrogen atom, an oxygen atom and a sulfur atom, and beingexemplified by imidazolyl, pyridyl, furyl, morpholino, benzoxazolyl,benzimidazolyl and benzothiazolyl). These substituents may further besubstituted. Also, in the case where two or more substituents exist,they may be the same or different from each other. Also, where possible,they may be connected to each other to form a ring.

[0034] The substituent represented by R^(Y1) is preferably an alkylgroup, an alkenyl group, an alkynyl group, an aryl group or a heteroring group, more preferably an alkyl group, an aryl group or an aromatichetero ring group, and still more preferably an alkyl group or an arylgroup.

[0035] X preferably represents an oxygen atom or N—R^(Y1), morepreferably an oxygen atom.

[0036] L represents a linking group of a conjugated bond. L ispreferably a conjugated bond type linking group formed by C, N, O, S,Se, Te, Si, Ge, etc., more preferably alkenylene, alkynylene, arylene, adivalent aromatic hetero ring (preferably an aromatic hetero ring formedby an azine ring, an azole ring, a thiophene ring or a furan ring) or agroup comprising a combination of N and one or more of these, still morepreferably alkenylene, arylene, a divalent aromatic hetero ring or agroup comprising N and one or more of these, particularly preferably agroup comprising a combination of alkenylene and arylene containing 6 to30 carbon atoms or a divalent aromatic hetero ring containing 2 to 30carbon atoms, most preferably a group comprising a combination ofalkenylene and arylene containing 6 to 30 carbon atoms.

[0037] Specific examples of the linking group represented by L includethe following:

[0038] R represents a hydrogen atom, an aliphatic hydrocarbyl group, anaryl group or a hetero ring group.

[0039] Ra and Rb each represents an aliphatic hydrocarbyl group, an arylgroup or a hetero ring group.

[0040] The linking group represented by L may have a substituent and, asthe substituent, there may be used, for example, those illustrated assubstituents represented by R¹ to R⁵. Preferred examples of thesubstituent represented by L include an alkyl group, an alkenyl group,an alkynyl group, an aryl group, an alkoxy group, an aryloxy group, anacyl group, a halogen atom, a cyano group, a hetero ring group and asilyl group, more preferred examples thereof include an alkyl group, analkenyl group, an alkynyl group, an aryl group, an alkoxy group, anaryloxy group, a halogen atom, a cyano group and an aromatic hetero ringgroup, and more preferred examples thereof include an alkyl group, anaryl group, an alkoxy group, an aryloxy group and an aromatic heteroring group.

[0041] R^(X) and R^(Y) may be the same or different from each other andeach represents a hydrogen atom or a substituent, with at least one ofthem representing an electron-withdrawing group. Also, R^(X) and R^(Y)may be connected to each other to form a ring.

[0042] As the substituents represented by R^(X) and R^(Y), there may beused, for example, those which have been illustrated as substituents ofR¹ to R⁵. Each of the substituents represented by R^(X) and R^(Y) ispreferably an alkyl group, an alkenyl group, an aryl group, an alkoxygroup, an aryloxy group, a carbonyl group, a thiocarbonyl group, anoxycarbonyl group, an acylamino group, a carbamoyl group, asulfonylamino group, a sulfamoyl group, a sulfonyl group, a sulfinylgroup, a phosphoryl group, an imino group, a cyano group, a halogenatom, a silyl group or an aromatic hetero ring group. More preferably,they are electron-withdrawing groups of 0.2 or more in Hammett's avalue. Still more preferably, each of them is an aryl group, an aromatichetero ring group, a cyano group, a carbonyl group, a thiocarbonylgroup, an oxycarbonyl group, a carbamoyl group, a sulfamoyl group, asulfonyl group, an imino group, a halogen atom or, when taken together,they form a ring of an electron-withdrawing group. Particularlypreferably, each of them is an aromatic hetero ring group, a carbonylgroup, a cyano group, an imino group or, when taken together, they forma ring of an electron-withdrawing group. Most preferably, each of themis a cyano group or, when taken together, they form a ring of anelectron-withdrawing group. Above all, R^(X) and R^(Y) are connected toeach other to form a ring of an electron-withdrawing group.

[0043] As a ring formed by R^(X) and R^(Y) connected to each othertogether with the carbon atom to which they are bound, those which areusually used as acid nuclei in merocyanine dyes are preferred. Specificexamples thereof are illustrated below.

[0044] (a) 1,3-dicarbonyl nucleus: for example, 1,3-indanedione,1,3-cyclohexanedione, 5,5-dimethyl-1,3-cyclohexanedione and1,3-dioxane-4,6-dione

[0045] (b) pyrazoline nucleus: for example,

[0046] 1-phenyl-2-pyrazolin-5-one, 3-methyl-1-phenyl-2-pyrazolin-5-oneand 1-(2-benzothiazolyl)-3-methyl-2-pyrazolin-5-one

[0047] (c) isoxazolinone nucleus: for example,

[0048] 3-phenyl-2-isoxazolin-5-one and 3-methyl-2-isoxazolin-5-one

[0049] (d) hydroxyindole nuclei: for example,1-alkyl-2,3-dihydro-2-hydroxyindole

[0050] (e) 2,4,6-triketohexahydropyrimidine nucleus: for example,

[0051] barbituric acid or 2-thiobarbituric acid and the derivativesthereof

[0052] Examples of the derivatives include 1-alkyl derivatives thereofsuch as 1-methyl and 1-ethyl derivatives thereof, 1,3-dialkylderivatives thereof such as 1,3-dimethyl, 1,3-diethyl and 1,3-dibutylderivatives thereof, 1,3-diaryl derivatives thereof such as1,3-diphenyl, 1,3-di(p-chlorophenyl) and 1,3-di(p-ethoxycarbonylphenyl)derivatives thereof, 1-alkyl-3-aryl derivatives thereof such as1-ethyl-3-phenyl derivative thereof, and 1,3-di-hetero ring substitutedderivatives thereof such as 1,3-di(2-pyridyl) derivative thereof.

[0053] (f) 2-thio-2,4-thiazolidinedione nucleus: for example,

[0054] rhodanine and the derivatives thereof

[0055] Examples of the derivatives include 3-alkylrhodanines such as3-methylrhodanine, 3-ethylrhodanine and 3-allylrhodanine,3-arylrhodanines such as 3-phenylrhodanine, and 3-heteroring-substituted rhodanines such as 3-(2-pyridyl)rhodanine.

[0056] (g) 2-thio-2,4-oxazolidinedione (2-thio-2,4-(3H,5H)-oxazoledione)nucleus: for example,

[0057] 3-ethyl-2-thio-2,4-oxazolinedione

[0058] (h) thianaphthene nucleus: for example,

[0059] 3(2H)-thianaphthenone-1,1-dioxide

[0060] (i) 2-thio-2,5-thiazolidinedione nucleus: for example,

[0061] 3-ethyl-2-thio-2,5-thiazolidinedione

[0062] (j) 2,4-thiazolidinedione nucleus: for example,

[0063] 2,4-thiazolidinedione, 3-ethyl-2,4-thiazolidinedione and3-phenyl-2,4-thiazolidinedione

[0064] (k) thiazolin-4-one nucleus: for example, 4-thiazolinone and2-ethyl-4-thiazolinone

[0065] (l) 4-thiazolidinone nucleus: for example,

[0066] 2-ethylmercapto-5-thiazolin-4-one and2-alkylphenylamino-5-thiazolin-4-one

[0067] (m) 2,4-imidazolidinedione (hydantoin) nucleus: for example,

[0068] 2,4-imidazolidinedione and 3-ethyl-2,4-imidazolidinedione

[0069] (n) 2-thio-2,4-imidazolidinedione (2-thiohydantoin) nucleus: forexample, 2-thio-2,4-imidazolidinedione and3-ethyl-2-thio-2,4-imidazolidinedione

[0070] (o) imidazolin-5-one nucleus: for example,

[0071] 2-propylmercapto-2-imidazolin-5-one

[0072] (p) 3,5-pyrazolidinedione nucleus: for example,

[0073] 1,2-diphenyl-3,5-pyrazolidinedione and1,2-dimethyl-3,5-pyrazolidinedione

[0074] The ring formed by R^(X), R^(Y) and the carbon atom to which theyare bound is preferably a 1,3-dicarbonyl nucleus, a pyrazolinonenucleus, a 2,4,6-triketohexahydropyrimidine nucleus (includingthioketone body), a 2-thio-2,4-thiazolidinedione nucleus, a2-thio-2,14-oxazolidinedione nucleus, a 2-thio-2,5-thiazolidinedionenucleus, a 2,4-imidazolidinedione nucleus, a2-thio-2,4-imidazolidinedione nucleus, a 2-imidazolin-5-one nucleus or a3,5-pyrazolidinedione nucleus, more preferably a 1,3-dicarbonyl nucleus,a 2,4,6-triketohexahydropyrimidine nucleus (including thioketonethereof) or a 3,5-pyrazolidinedione nucleus, particularly preferably a1,3-dicarbonyl nucleus or a 2,4,6-triketohexahydropyrimidine nucleus(including thioketone body), most preferably a 1,3-indanedione nucleus.

[0075] Of the compounds represented by the general formula (I), thoserepresented by the general formula (II) are preferred.

[0076] In the formula, R¹, R², R³, R⁴, R⁵ and X each is the same asdefined with respect to the general formula (I), with preferred scopesthereof also being the same. Z² represents atoms necessary for forming a5- or 6-membered ring.

[0077] Preferred examples of the ring formed by Z² include a1,3-dicarbonyl nucleus, a pyrazolinone nucleus, a2,4,6-triketohexahydropyrimidine nucleus (including thioketone body), a2-thio-2,4-thiazolidinedione nucleus, a 2-thio-2,4-oxazolidinedionenucleus, a 2-thio-2,5-thiazolidinedione nucleus, a 2,4-thiazolidinedionenucleus, a 2,4-imidazolidinedione nucleus, a2-thio-2,4-imidazolidinedione nucleus and a 1,3-pyrazolidinedionenucleus, more preferred examples thereof include a 1,3-dicarbonylnucleus and a 2,4,6-triketohexahydropyrimidine nucleus (includingthioketone body), still more preferred examples thereof include a1,3-dicarbonyl nucleus, a barbituric acid derivative and a2-thiobarbituric acid derivative, and particularly preferred example isa 1,3-dicaqrbonyl nucleus (preferably a 1,3-indanedione nucleus).

[0078] The ring formed by Z² may have a substituent and, as suchsubstituent, there may be used, for example, those illustrated assubstituents for R¹ and R².

[0079] L₂₁ and L₂₂, which may be the same or different from each other,each represents a methine group, a substituted methine group or anitrogen atom, or L₂₁s, or L₂₂s, may be connected to each other, or L₂₁and L₂₂ are connected to each other, via the substituent of thesubstituted methine group to form a 4- to 6-membered ring. Further,where possible, L₂₁ or L₂₂ may be connected to Ar or R³ to form a ring.

[0080] As the substituent for the substituted methine group, there maybe used, for example, those which are illustrated as substituentsrepresented by R¹ to R⁵. Preferred examples thereof include an alkylgroup, an aryl group, an aralkyl group, an alkoxy group, an aryloxygroup, an alkylthio group, an arylthio group, a cyano group and ahalogen atom, and more preferred examples thereof include an alkyl groupand an alkoxy group, with a lower alkyl group (containing preferably 1to 4 carbon atoms) being still more preferred.

[0081] L₂₁ and L₂₂ are preferably a non-substituted methine group, analkyl-substituted methine group or an alkoxy-substituted methine group,more preferably a non-substituted methine group, or L₂₂ is connected toAr via the substituent to forms a 5- or 6-membered ring, still morepreferably a non-substituted methine group.

[0082] n represents an integer of 0 to 3, preferably 0, 1 or 2, morepreferably 0 or 1,still more preferably 1.

[0083] Ar represents an arylene group or a divalent aromatic hetero ringgroup. The aryelne group or the divalent aromatic hetero ring grouprepresented by Ar may have a substituent and, as examples of thesubstituent, there may be illustrated, for example, those referred to assubstituents of R¹ to R⁵. Preferred examples of the substituent for Arinclude an alkyl group, an alkenyl group, an alkynyl group, an arylgroup, an alkoxy group, an aryloxy group, an acyl group, a halogen atom,a cyano group, a hetero ring group and a silyl group, more preferredexamples thereof include an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, an alkoxy group, an aryloxy group, a halogen atom,a cyano group and an aromatic hetero ring group, more preferred examplesthereof include an alkyl group, an aryl group, an alkoxy group and anaromatic hetero ring group, and particularly preferred examples thereofinclude an alkyl group containing 1 to 6 carbon atoms and an alkoxygroup containing 1 to 6 carbon atoms.

[0084] Of the compounds represented by the general formula (II), thoserepresented by the general formula (III) are more preferred.

[0085] In the formula, R¹, R², R³, R⁴and R⁵ are respectively the same asthose defined with respect to the general formula (I), with preferredscopes thereof also being the same. L₂₁, L₂₂ and n are respectively thesame as those defined with respect to the general formula (II), withpreferred scopes thereof also being the same. R³¹, R³², R³³ and R³⁴ eachrepresents a hydrogen atom or a substituent. As the substituentrepresented by R³¹ to R³⁴, there may be used, for example, those whichare illustrated as substituents of R¹ to R⁵ in the general formula (I).Z³ represents atoms necessary for forming a 5- or 6-membered ring. Asthe ring formed by Z³, there are illustrated, from among the examples ofthe ring formed by Z² in the general formula (II), those which have a1,3-dicarbonyl structure within the ring. Examples thereof include1,3-cyclopentanedione, 1,3-cyclohexanedione, 1,3-indanedione and3,5-pyrazolidinedione, preferred examples thereof include1,3-indanedione and 3,5-pyrazolidinedione, more preferred examplesthereof include 1,3-indanedione and 1,2-diaryl-3,5-pyrazolidinedione,and still more preferred examples thereof include 1,3-indanedione and1,2-diphenyl-3,5-pyrazolidinedione, with 1,3-indanedione beingparticularly preferred.

[0086] The ring formed by Z³ may have a substituent and, as suchsubstituent, there may be used, for example, those illustrated assubstituents for R¹ to R⁵.

[0087] Of the compounds represented by the general formula (III), thoserepresented by the general formula (IV) are more preferred.

[0088] In the formula, R¹, R², R³, R⁴, R⁵ and R⁶ are respectively thesame as those defined with respect to the general formula (I), withpreferred scopes thereof also being the same. R³¹, R³², R³³ and R³⁴ arerespectively the same as those defined with respect to the generalformula (III), with preferred scopes thereof also being the same. R⁴¹,R⁴², R⁴³ and R⁴⁴ each represents a hydrogen atom or a substituent. Asthe substituent represented by R⁴¹, R⁴², R⁴³ and R^(44,)there may beapplied, for example, those which are illustrated as substituents of R¹to R⁵ in the general formula (I). Also, where possible, R⁴¹, R⁴², R⁴³and R⁴⁴ may be connected to each other to form a ring. Preferredexamples of R⁴¹ to R⁴⁴ include a hydrogen atom, an alkyl group(containing preferably 1 to 20 carbon atoms, more preferably 1 to 12carbon atoms, still more preferably 1 to 8 carbon atoms), an aryl group(containing preferably 6 to 30 carbon atoms, more preferably 6 to 20carbon atoms, still more preferably 6 to 12 carbon atoms), a hetero ringgroup (containing preferably 2 to 30 carbon atoms, more preferably 2 to20 carbon atoms, still more preferably 2 to 12 carbon atoms), a halogenatom, a cyano group, an alkoxy group (containing preferably 1 to 20carbon atoms, more preferably 1 to 12 carbon atoms, still morepreferably 1 to 8 carbon atoms), an aryloxy group (containing preferably6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, still morepreferably 6 to 12 carbon atoms), an alkoxycarbonyl group (containingpreferably 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms,still more preferably 1 to 8 carbon atoms), an aryloxycarbonyl group(containing preferably 6 to 30 carbon atoms, more preferably 6 to 20carbon atoms, still more preferably 6 to 12 carbon atoms), and a benzenering or an aromatic azole ring formed by R⁴² and R⁴³ connected to eachother. More preferred examples thereof include a hydrogen atom, an alkylgroup, an aryl group, a hetero ring group, a halogen atom, a cyanogroup, and a benzene ring formed by R⁴² and R⁴³ connected to each other,with a hydrogen atom being particularly preferred.

[0089] R^(A1) and R^(A2) each represents a hydrogen atom or asubstituent or, where possible, R^(A1) and R^(A2) are connected to eachother or to other substituent to form a ring. As the substituentrepresented by R^(A1) and R^(A2), there may be applied, for example,those which are illustrated as substituents of R¹ to R⁵ in the generalformula (I). Preferred examples of R^(A1) and R^(A2) include a hydrogenatom, an alkyl group, an aryl group, an aralkyl group, an alkoxy group,an aryloxy group, an alkylthio group, an arylthio group, a cyano groupand a halogen atom, and more preferred examples thereof include an alkylgroup and an alkoxy group, with a lower alkyl group (containingpreferably 1 to 4 carbon atoms) being still more preferred.

[0090] Also, the compounds represented by the general formula (I) may below molecular weight compounds, high molecular weight compounds (havinga weight-average molecular weight of preferably 1000 to 5000000, morepreferably 5000 to 2000000, still more preferably 10000 to 1000000)wherein the residue is connected to the main chain of the polymer, orhigh molecular weight compounds (having a weight-average molecularweight of preferably 1000 to 5000000, more preferably 5000 to 2000000,still more preferably 10000 to 1000000) which have the compoundrepresented by the general formula (I) in the main chain thereof. Thehigh molecular weight compounds may be homopolymers or copolymers withother polymer. The copolymers may be random copolymers or blockcopolymers. As the compounds to be used in the invention, low molecularweight compounds are preferred.

[0091] Also, the compounds represented by the general formula (I) may becontained in a state of forming a metal chelate.

[0092] Specific examples of the compounds of the invention representedby the general formula (I), there may be illustrated, for example, thosewhich are described in JP-A11-292875,JP-A-11-335661,JP-A-11-335368,Japanese Patent Application No. H11-161130, Japanese Patent ApplicationNo. H11-264380 and Japanese Patent Application No. 2001-16980. Morepreferred specific examples are illustrated below which, however, do notlimit the invention in any way.

[0093] The above-described compounds may be used in the form of thetautomers or metal complexes thereof as the light-emitting materials.

[0094] The compounds of the invention represented by the general formula(I) may be synthesized by reference to, for example, processes describedin JP-A-11-335661,JP-A-11-292875,JP-A-11-335368, Japanese PatentApplication No. H11-161130, Japanese Patent Application No. H11-264380and Japanese Patent Application No. 2001-16980.

[0095] The content of at least one compound selected from the compoundsrepresented by the general formulae (I) to (IV) in the light-emittinglayer is preferably 0.01% by weight to 50% by weight, more preferably0.1% by weight to 10% by weight, still more preferably 0.3% by weight to5% by weight.

[0096] Next, the organic membrane existing in contact with thelight-emitting layer containing both the light-emitting materialselected from the compounds of the invention represented by the generalformula (I) and the host material and existing between thelight-emitting layer and a cathode is described. The organic membrane ofthe invention has electron-transporting properties and has a largerionization potential than the ionization potential of the host materialin the light-emitting layer.

[0097] The ionization potential values of the organic membrane and thehost material can be obtained by a method of preparing a single-layermembrane of the organic membrane and a single-layer membrane of the hostmaterial and measuring the ionization potential in a membrane stateusing a photo-electron spectrometer (made by Riken Keiki; &AC-1) or by amethod of determining the oxidation potential according to the cyclicvoltammetry and calculating the ionization potential as a solution.

[0098] The difference in ionization potential between the organicmembrane and the host material in the light-emitting layer is preferably0.01 eV to 2 eV, more preferably 0.1 eV to 2 eV, particularly preferably0.2 eV to 2 eV. In contrast, in case where there exists no differencetherebetween in ionization potential or where the ionization potentialof the host material is larger, there results a deterioratedlight-emitting efficiency and a poor response upon pulse driving,particularly a large temperature dependence of the photo pulse width.

[0099] The ionization potential of the organic membrane is preferablymore than 5.7 eV and not exceeding 7.0 eV, more preferably 5.8 eV to 6.9eV, still more preferably 5.9 eV to 6.8 eV, particularly preferably 6.0eV to 6.8 eV.

[0100] Also, an electron transporting and electron injecting membranemay be provided between the organic membrane and the cathode, with knownelectron transporting and injecting materials being used.

[0101] The organic membrane-constituting compounds are preferably heteroring compounds containing at least two hetero atoms, metal complexescontaining a nitrogen-containing hetero ring and having a ligand, styrylderivatives and aryl-substituted arylene derivatives, more preferablyhetero ring compounds containing at least two hetero atoms, metalcomplexes containing a nitrogen-containing hetero ring and having aligand, and styryl derivatives, particularly preferably hetero ringcompounds containing at least two hetero atoms.

[0102] The hetero ring compounds containing at least two hetero atomsare those compounds which have two or more atoms other than carbon atomand hydrogen atom within the fundamental skeleton, and may be of asingle ring system or a fused ring system. The hetero ring skeleton hastwo or more atoms preferably selected from N, O and S atoms. Morepreferably, it is an aromatic hetero ring containing at least one N atomwithin the skeleton, with an aromatic hetero ring having two or more Natoms within the skeleton being particularly preferred. Also, the heteroatoms may exist either at the fused position or at non-fused position.

[0103] Examples of the hetero ring skeleton containing two or morehetero atoms include pyrazole, imidazole, oxazole, thiazole, triazole,oxadiazole, thiadiazole, pyrazine, pyrimidine, indazole, purine,phthalazine, naphthylidine, quinoxaline, quinazoline, cinnoline,pteridine, perimidine, phenanthroline, pyrroloimidazole,pyrrolotriazole, pyrazoloimidazole, pyrazolotriazole,pyrazolopyrimidine, pyrazolotriazine, imidazoimidazole,imidazopyridazine, imidazopyridine, imidazopyrazine, triazolopyridine,benzimidazole, naphthimidazole, benzoxazole, naphthoxazole,benzothiazole, naphthothiazole, benzotriazole, tetrazaindfene andtriazine. Preferred examples thereof include triazole, oxadiazole,thiadiazole, imidazopyridazine, imidazopyridine, imidazopyrazine,benzimidazole, naphthimidazole, benzoxazole, naphthoxazole,benzothiazole, naphthothiazole and triazine. More preferred examplesthereof include imidazopyridine, imidazopyrazine, benzimidazole andnaphthimidazole. Still more preferred examples thereof includeimidazopyridine, benzimidazole, naphtimidazole and triazine, withimidazopyridine being particularly preferred.

[0104] Preferred compounds having a hetero ring skeleton containing twoor more hetero atoms are compounds represented by the following generalformula (V) or (VI):

L⁶-(A)_(m)6   general formula (VI)

[0105] In the general formula (V), R⁵⁵ and R⁵⁶, which may be the same ordifferent from each other, each represents an alkyl group, an aryl groupor a hetero ring group, X⁵ represents an oxygen atom, a sulfur atom orNR^(Y5), R^(Y5) represents a hydrogen atom or a substituent (an alkylgroup, an alkenyl group, an alkynyl group, an aryl group or a heteroring group) . Here, the alkyl group, the alkenyl group, the alkynylgroup, the aryl group and the hetero ring group are the same asdescribed with respect to R1 to R⁵ in the general formula (I), withpreferred scopes thereof also being the same as described there.

[0106] In the general formula (VI), A represents a hetero ring groupcontaining two or more hetero atoms, and a plurality of hetero ringgroups represented by A maybe the same or different from each other. m⁶represents an integer of 2 or more. L⁶ represents a linking group.

[0107] The linking group represented by L⁶ is preferably a linking groupformed by a single bond, C, N, O, S, Si or Ge, more preferably a singlebond, alkylene, alkenylene, alkynylene, arylene, a divalent hetero ring(preferably an aromatic hetero ring, more preferably an aromatic heteroring formed by an azole ring, a thiophene ring or a furan ring) or agroup comprising a combination of N and these, still more preferablyarylene, a divalent aromatic hetero ring or a group comprising acombination of N and these.

[0108] As the specific examples of the linking group represented by L⁶,there are illustrated, for example, the following as well as the singlebond.

[0109] m⁶ represents an integer of 2 or more, preferably 2 to 8, morepreferably 2 to 6, still more preferably 2 to 4,particularly preferably2 or 3, most preferably 3.

[0110] As the hetero ring group represented by Ar and containing two ormore hetero atoms, there are preferably illustrated the compoundsrepresented by the following general formula (E11):

[0111] general formula (E11)

[0112] wherein X^(E) represents O, S, N—R^(a) or C—R^(a), R^(a)represents a hydrogen atom or a substituent (an aliphatic hydrocarbylgroup, an aryl group or a hetero ring group), Q represents atomsnecessary to form a hetero ring together with N and X^(E).

[0113] The aliphatic hydrocarbyl group represented by R^(a) is astraight, branched or cyclic alkyl group (containing preferably 1 to 20carbon atoms, more preferably 1 to 12 carbon atoms, particularlypreferably 1 to 8 carbon atoms and being exemplified by methyl, ethyl,iso-propyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl,cyclopentyl and cyclohexyl), an alkenyl group (containing preferably 2to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularlypreferably 2 to 8 carbon atoms and being exemplified by vinyl, allyl,2-butenyl and 3-pentenyl) or an alkynyl group (containing preferably 2to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularlypreferably 2 to 8 carbon atoms and being exemplified by propargyl and3-pentynyl) and, more prefrerably, an alkyl group.

[0114] The aryl group represented by Ra is a single ring or fused ringaryl group containing preferably 6 to 30 carbon atoms, more preferably 6to 20 carbon atoms, still more preferably 6 to 12 carbon atoms and isexemplified by phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl,2-methoxyphenyl, 3-trifluoromethylphenyl, pentafluorophenyl, 1-naphthyland 2-naphthyl.

[0115] The hetero ring group represented by R^(a) is a single heteroring or fused hetero ring group (containing preferably 1 to 20 carbonatoms, more preferably 1 to 12 carbon atoms, still more preferably 2 to10 carbon atoms) and is preferably an aromatic hetero ring groupcontaining at least one of a nitrogen atom, an oxygen atom, a sulfuratom and a selenium atom. Specific examples of the hetero ring grouprepresented by R^(a) include pyrrolidine, piperazine, morpholine,thiophene, selenophene, furan, pyrrole, imidazole, pyrazole, pyridine,pyrazine, pyridazine, pyrimidine, triazole, triazine, indole, indazole,purine, thiazoline, thiazole, thiadiazole, oxazoline, oxazole,oxadiazole, quinoline, isoquinoline, phthalazine, naphthyridine,quinoxaline, quinazoline, cinnoline, pteridine, acridine,phenanthroline, phenazine, tetrazole, benzimidazole, benzoxazole,benzothiazole, benzotriazole, tetrazaindene, carbazole and azepine.Preferred examples thereof include furan, thiophene, pyridine,ppyrazine, pyrimidine, pyridazine, triazine, quinoline, phthalazine,naphthyridine, quinoxaline and quinazoline, and more preferred examplesthereof include furan, thiophene, pyridine and quinoline, with quinolinebeing still more preferred.

[0116] The aliphatic hydrocarbyl group, the aryl group or the heteroring group represented by R^(a) may have a substituent. As suchsubstituent, those illustrated as substituents represented by R¹ to R⁵in the general formula (I) maybe applied, with a preferred scope thereofbeing also the same.

[0117] R^(a) is preferably an alkyl group, an aryl group or an aromatichetero ring group, more preferably an aryl group or an aromatic heteroring group, still more preferably an aryl group.

[0118] X^(E) is preferably O or N—R^(a), more preferably N—R^(a),particularly preferably N—Ar (Ar being an aryl group (containingpreferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms,still more preferably 6 to 12 carbon atoms) or an aromatic hetero ringgroup (containing preferably 1 to 20 carbon atoms, more preferably 1 to12 carbon atoms, still more preferably 2 to 10 carbon atoms), preferablyan aryl group).

[0119] Q represents atoms necessary for forming a hetero ring by beingconnected to N and X^(E). The hetero ring formed by Q is preferably anaromatic hetero ring, more preferably a 5- to 8-membered hetero ring,more preferably a 5- or 6-membered aromatic hetero ring, particularlypreferably a 5-membered aromatic hetero ring.

[0120] Specific examples of the hetero ring formed by Q include animidazole ring, an oxazole ring, a thiazole ring, a selenazole ring, atellurazole ring, a triazole ring, a tetrazole ring, anoxadizole ring, athiadiazole ring, an oxatriazole ring, a thiatriazole ring, a pyridinering, a pyrazine ring, a pyridazine ring and a pyrimidine ring, morepreferred examples thereof include an imidazole ring, an oxazole ring, athiazole ring, an oxadiazole ring and a thiadiazole ring, and morepreferably an imidazole ring and an oxazole ring, with an imidazole ringbeing still more preferred.

[0121] The hetero ring formed by Q may form a fused ring together withother ring, and may have a substituent. As the substituent, thoseillustrated as substituents represented by R¹ to R⁵ in the generalformula (I) may be applied. Preferred examples of the substituent for Qinclude an alkyl group, an alkenyl group, an alkynyl group, an arylgroup, an amino group, an alkoxy group, an aryloxy group, an acyl group,an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, anacylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoylgroup, an alkylthio group, an arylthio group, a sulfonyl group, ahalogen atom, a cyano group and a hetero ring group, more preferredexamples thereof include an alkyl group, an alkenyl group, an arylgroup, an alkoxy group, an aryloxy group, a halogen atom, a cyano groupand a hetero ring group, still more preferred examples thereof includean alkyl group, an aryl group, an alkoxy group, an aryloxy group and anaromatic hetero ring group, and particularly preferred examples thereofinclude an alkyl group, an aryl group, an alkoxy group and an aromatichetero ring group.

[0122] Of the compounds represented by the general formula (VI),preferred compounds are those represented by the following generalformula (E12):

[0123] general formula (E12):

[0124] wherein L⁶ and m⁶ are the same as defined with respect to thosein the general formula (VI), X^(E) is the same as defined with respectto the general formula (E11), and preferred scopes thereof are also thesame. Z^(b) represents atoms necessary for form an aromatic ring. Thearomatic ring formed by Z^(b) may be an aromatic hydrocarbon ring or anaromatic hetero ring. Specific examples thereof include a benzene ring,a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring,a pyrrole ring, a furan ring, a thiophene ring, a selenophene ring, atellurophene ring, an imidazole ring, a thiazole ring, a selenazolering, a tellurazole ring, a thiadiazole ring, an oxadiazole ring and apyrazole ring, preferred examples thereof include a benzene ring, apyridine ring, a pyrazine ring, a pyrimidine ring and a pyridazine ring,more preferred examples thereof include a benzene ring, a pyridine ringand a pyrazine ring, and still more preferred examples thereof include abenzene ring and a pyridine ring, with a pyridine ring beingparticularly preferred.

[0125] The aromatic ring formed by Z^(b) may form a fused ring togetherwith other ring, and may have a substituent. As the substituent, thoseillustrated as substituents represented by R¹ to R⁵ in the generalformula (I) may be applied. Preferred examples of the substituent forthe aromatic ring formed by Z^(b) include an alkyl group, an alkenylgroup, an alkynyl group, an aryl group, an amino group, an alkoxy group,an aryloxy group, an acyl group, an alkoxycarbonyl group, anaryloxycarbonyl group, an acyloxy group, an acylamino group, analkoxycarbonylamino group, an aryloxycarbonylamino group, asulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthiogroup, an arylthio group, a sulfonyl group, a halogen atom, a cyanogroup and a hetero ring group, more preferred examples thereof includean alkyl group, an alkenyl group, an aryl group, an alkoxy group, anaryloxy group, a halogen atom, a cyano group and a hetero ring group,still more preferred examples thereof include an alkyl group, an arylgroup, an alkoxy group, an aryloxy group and an aromatic hetero ringgroup, and particularly preferred examples thereof include an alkylgroup, an aryl group, an alkoxy group and an aromatic hetero ring group.

[0126] Of the compounds represented by the general formula (VI), stillmore preferred are those compounds which are represented by the generalformula (E13):

[0127] wherein L⁶, X^(E) and m⁶ are the same as those in the generalformulae (VI) and (E11), and preferred scopes thereof are also the same.Z^(b3) represents atoms necessary for forming an aromatic hetero ring.The aromatic hetero ring formed by Z^(b3) is preferably a 5- or6-membered aromatic hetero ring, more preferably a 5- or 6-membered,nitrogen-containing aromatic hetero ring, still more preferably a6-membered, nitrogen-containing aromatic hetero ring. Specific examplesof the aromatic hetero ring formed by Z^(b3) include furan, thiophene,pyran, pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine,pyridazine, thiazole, oxazole, isothiazole, isoxazole, thiadiazole,oxadiazole, triazole, selenazole and tellurazole, preferred examplesthereof include pyridine, pyrazine, pyrimidine and pyridazine, and stillmore preferred examples thereof include pyridine and pyrazine, withpyridine being particularly preferred. The aromatic ring formed byZ^(b3) may form a fused ring together with other ring, and may have asubstituent. As the substituent, those illustrated as substituentsrepresented by R¹ to R⁵in the general formula (I) may be applied, andpreferred scopes thereof are also the same as described there.

[0128] Of the compounds represented by the general formula (VI), stillmore preferred are those which are represented by the general formula(E14):

[0129] wherein L⁶and m⁶ are the same as those in the general formulae(VI), and preferred scopes thereof are also the same. Z^(b7) representsatoms necessary for forming a 6-membered, nitrogen-containing aromatichetero ring. Specific examples of the 6-membered, nitrogen-containingaromatic hetero ring formed by Z^(b7) include pyridine, pyrazine,pyrimidine, pyridazine and triazine, preferred examples thereof includepyridine, pyrazine, pyrimidine and pyridazine, and still more preferredexamples thereof include pyridine and pyrazine, with pyridine beingparticularly preferred. The 6-membered, nitrogen-containing aromaticring formed by Z^(b7) may form a fused ring together with other ring,and may have a substituent.

[0130] Of the compounds represented by the general formula (VI), morepreferred are those compounds which are represented by the followinggeneral formula (E15):

[0131] wherein R^(b81), R^(b82) and R^(b83) are the same as R^(a) in thegeneral formulae (E11), and preferred scopes thereof are also the same.Z^(b81) Z^(b82) and Z^(b83) are the same as Z^(b3) in the generalformula (E13), and preferred scopes thereof are also the same. L¹, L²and L³ are the same as L⁶ defined in the general formula (VI). L¹, L²and L³ are a single bond, arylene, a divalent aromatic hetero ring and alinking group composed of a combination of these, more preferably are asingle bond, benzene, naphthalene, anthracene, pyridine, pyrazine,thiophene, furan, oxazole, thiazole, oxadiazole, thiadiazole, triazoleand a linking group composed of these, still more preferably a singlebond, benzene, thiophene and a linking group composed of a combinationof these, and particularly preferably a single bond, benzene and alinking group composed of a combination of these, with a single bondbeing most preferred. L¹, L² and L³ may have a substituent and, as thesubstituent, there may be applied those which have been illustrated asR¹ to R⁵in the general formula (I), with preferred scopes thereof beingthe same.

[0132] YE represents a nitrogen atom or a 1,3,5-benzenetriyl group, withthe latter optionally having a substituent. Examples of the substituentinclude an alkyl group, an aryl group and a halogen atom. Y^(E) ispreferably a nitrogen atom or an unsubstituted 1,3,5-benzenetriyl group,more preferably an unsubstituted 1,3,5-benzenetriyl group.

[0133] Next, the metal complex having a ligand containing anitrogen-containing hetero ring compound is described below. Examples ofthe nitrogen-containing hetero ring skeleton include pyrazole,imidazole, oxazole, thiazole, triazole, oxadiazole, thiadiazole,pyridine, pyrazine, pyrimidine, pyridazine, quinoline, isoquinoline,indazole, purine, phthalazine, napohthylidine, quinoxaline, quinazoline,cinnoline, pteridine, perimidine, phenanthroline, pyrroloimidazole,pyrrolotriazole, pyrazoloimidazole, pyrazolotriazole,pyrazolopyrimidine, pyrazolotriazine, imidazoimidazole,imidazopyridazine, imidazopyridine, imidazopyrazine, triazolopyridine,benzimidazole, naphthimidazole, benzoxazole, naphthoxazole,benzothiazole, naphthothiazole, benzotriazole, tetrazaindene andtriazine. Preferred examples thereof are triazole, oxazole, oxadiazole,thiadiazole, imidazopyridazine, imidazopyridine, imidazopyrazine,benzimidazole, naphthimidazole, benzoxazole, naphthoxazole,benzothiazole, naphthothiazole, pyridine, quinoline and triazine. Stillmore preferred examples are triazole, oxazole, oxadiazole, pyridine,quinoline and triazine. Particularly preferred examples are triazole,oxazole, oxadiazole, pyridine and quinoline.

[0134] The ligand contained in the metal complex preferably has analkoxy group, an aryloxy group, a heteroaryloxy group, a sulfonamidegroup or an amido group in addition to the nitrogen atom of thenitrogen-containing hetero ring as coordinating groups to form abidendate ligand. The metal complex is preferably a compound representedby the general formula (E21) or (E22).

[0135] In the general formula (E21) or (E22), Z^(E1) and Z^(E4) eachrepresents atoms necessary for forming a 5- to 6-membered,nitrogen-containing aromatic hetero ring. Specific examples of thenitrogen-containing aromatic hetero ring represented by Z^(E1) or Z^(E4)include an imidazole ring, an oxazole ring, a thiazole ring, aselenazole ring, a tellurazole ring, a triazole ring, a tetrazole ring,an oxadiazole ring, a thiadiazole ring, a pyridine ring, a pyrazinering, a pyridazine ring and a pyrimidine ring.

[0136] At least one of Z^(E2) and Z^(E3) represents atoms for forming anaryl group or a 5- to 6-membered aromatic hetero ring group. Z^(E5)represents atoms for forming an aryl group or a 5- to 6-memberedaromatic hetero ring group. As the aryl group or the 5- to 6-memberedaromatic hetero ring group formed by Z^(E2), Z^(E3) or Z^(E5), there areillustrated a benzene ring, an imidazole ring, an oxazole ring, athiazole ring, a selenazole ring, a tellurazole ring, a triazole ring, atetrazole ring, an oxadiazole ring, a thiadiazole ring, an oxatriazolering, a thiatriazole ring, a pyridine ring, a pyrazine ring, apyridazine ring and a pyrimidine ring. Y^(E1) and Y^(E2) each representsan oxygen atom, a dissociated sulfonamide group or a dissociatedacylamino group, and may be connected to Z^(E3) or Z^(E5) to form aring. The dissociated sulfonamido group and the dissociated acylaminogroup represented by Y^(E1) or Y^(E2) are those of the sulfonamide groupand the acylamino group represented by R¹ to R⁵ from which adissociatable hydrogen atom is dissociated. Y^(E1) and Y^(E2) eachpreferably represents an oxygen atom or a dissociated sulfonamide group,more preferably an oxygen atom. L^(E) represents an alkoxy group, anaryloxy group, a heteroaryloxy group or a hydroxyl group. nE1 and nE3each represents 2 or 3, and mE2 and mE4 each represents 0 or 1. Mrepresents a metal atom, preferably aluminum, zinc, boron or beryllium.The general formula (E21) preferably represents a compound representedby the general formula (VIII) and, of the compounds represented by thegeneral formula (E22), preferred are compounds represented by thegeneral formula (VII) or (VIII).

[0137] In the general formula (VII), R⁷¹ represents a substituent, R⁷²represents a hydrogen atom, an aliphatic group, an aryl group or anaromatic hetero ring group, M represents a metal atom, and n⁷ representsan integer of 0 to 6, m⁷ represents 2 or 3, provided that, when m⁷=3,then n⁷≠0. When n⁷ represents an integer of 2 to 6, a plurality of R⁷¹smay be the same or different, and may be connected to each other to forma ring. As the substituent represented by R⁷¹, those illustrated assubstituents represented by R¹ to R⁵in the general formula (I) may beapplied, with preferred examples thereof also being the same. Morepreferably, R⁷¹ is an aliphatic group, an aryl group or a hetero ringgroup. R⁷² is preferably a hydrogen atom, an aryl group or an aromatichetero ring group. In the general formula (VIII), X⁸¹ represents anitrogen atom or C—R⁸¹, X⁸² represents an oxygen atom, a sulfur atom orN—R^(Y8), R⁸¹, R⁸², R⁸³ and R^(Y8) each represents a hydrogen atom or asubstituent. R⁸¹ and R⁸² may be connected to each other to form a ring.R⁸⁴ represents a hydrogen atom, an aliphatic group, an aryl group or anaromatic hetero ring group, and M represents a metal atom, preferablyaluminum, zinc, boron or beryllium. n8 represents an integer of 0 to 4.m⁸ represents 2 or 3. When n⁸ represents an integer of 2 to 4, pluralR⁸³s may be the same or different from each other, and may be connectedto each other to form a ring. Preferred scopes of R⁸³ and R⁸⁴ are thesame as those of R⁷¹ and R⁷², respectively. The nitrogen-containinghetero ring formed by X⁸¹ and X⁸² is preferably an imidazole ring, anoxazole ring, a thiazole ring, a selenazole ring, a tellurazole ring, atriazole ring, a tetrazole ring, an oxadiazole ring or a thiadiazolering, more preferably an imidazole ring, an oxazole ring, a thiazolering, a triazole ring, a tetrazole ring, an oxadiazole ring or athiadiazole ring. R⁸¹ and R⁸² are the same as defined for R¹ to R⁵ inthe general formula (I), with preferred scopes thereof being also thesame. R⁸¹ and R⁸² each preferably represents an aliphatic group, an arylgroup or an aromatic hetero ring group.

[0138] Next, descriptions on the styryl derivatives are given below. Thestyryl derivatives are preferably those compounds which are representedby the general formula (IX) or (X).

[0139] In the general formula (IX), R⁹¹ represents a substituent. R⁹² toR⁹⁴ each represents a hydrogen atom or a substituent, and a plurality ofR⁹¹s may be connected to each other to form a fused ring. m⁹ representsan integer of 0 to 5. As the substituents represented by R⁹¹ to R⁹⁴,there are illustrated, for example, those illustrated as substituents ofR¹ to R⁵, with preferred examples thereof being the same. Preferredexamples of R⁹¹ and R⁹² include an alkyl group, an alkenyl group, analkynyl group, an aryl group, an aromatic hetero ring group and a silylgroup, more preferred examples thereof include a hydrogen atom, an alkylgroup, an aryl group, an aromatic hetero ring group and a silyl group,and particularly preferred examples thereof include a hydrogen atom, anaromatic hetero ring group and a silyl group. When m⁹ represents 2 to 5,a plurality of R⁹¹s maybe the same or different from each other, andmaybe connected to each other to form a ring. Preferred examples of R⁹³and R⁹⁴ include a hydrogen atom, an alkyl group, an aryl group and anaromatic hetero ring group.

[0140] In the general formula (X), R¹⁰¹ and R¹⁰² each represents ahydrogen atom or a substituent, and R¹⁰³ to R¹⁰⁶ each represents asubstituent. L¹⁰ represents a linking group, m¹⁰, n¹⁰, p¹⁰ and q¹⁰ eachrepresents an integer of 0 to 5. As the substituents represented by R¹⁰¹to R¹⁰⁶, there are illustrated, for example, those illustrated assubstituents of R¹ to R⁵, with preferred scopes thereof being the same.When m¹⁰, n¹⁰ p¹⁰ and q¹⁰ each represents 2 to 5, a plurality of R¹⁰³ toR¹⁰⁶ may be the same or different from each other, and may be connectedto each other to form a fused ring. Also, R¹⁰³ and R¹⁰⁴, or R¹⁰³ andR¹⁰⁴, may be connected to each other to form a ring. Preferred examplesof R¹⁰¹ and R¹⁰² include a hydrogen atom, an alkyl group, an aryl groupand an aromatic hetero ring group, with a hydrogen atom beingparticularly preferred. Specific examples of the linking grouprepresented by L¹⁰ are the same as the specific examples of L⁶ in thegeneral formula (VI).

[0141] Next, the aryl-substituted arylene derivative is described below.The aryl-substituted arylene derivative represents that wherein arylgroups are connected by an arylene group. As specific examples of thearylene group, there are illustrated those arylene groups which havebeen illustrated as linking groups represented by L6 in the generalformula (VI), with 2- or 3-valent arylene groups being preferred. Thearyl-substituted arylene derivatives are preferably compoundsrepresented by the general formula (XI).

[0142] general formula (XI)

[0143] In the general formula (XI), specific examples of Ar¹¹¹ includethe 3-valent arylene groups illustrated as linking groups represented byL⁶ in the general formula (VI), with a 1,3,5-benzenetriyl group beingmore preferred. Ar¹¹² to Ar¹¹⁴ each represents an aryl group containingpreferably 6 to 40 carbon atoms, more preferably 6 to 30 carbon atoms,particularly preferably 6 to 20 carbon atoms, and are exemplified byphenyl, p-methylphenyl, naphthyl, anthryl, phenanthryl and pyrenyl.Ar¹¹² to Ar¹¹⁴ may further be substituted, with preferred substituentsbeing an alkyl group, an aryl group, an aromatic hetero ring group and asilyl group.

[0144] The content of at least one compound selected from the compoundsrepresented by the general formula (V) to (XI) in the organic membraneis preferably 50% by weight to 100% by weight, more preferably 90% byweight to 100% by weight, still more preferably 100% by weight or less.As other components of the organic membrane, materials having nocharge-transporting properties may be contained.

[0145] Specific examples of the compound constituting the organicmembrane in contact with the light-emitting layer containing thelight-emitting material of the invention represented by the generalformula (I) and between the light-emitting layer and a cathode areillustrated below. In addition to them, there may be illustrated thosedescribed in Japanese Patent Application Nos. 2000-254171, 2000-290626,2000-38578, 2000-111014,H11-108207, H11-217820, H11-36107 andH11-232744,JP-A-2000-229966, JP-A-2000-229957,JP-A-2000-229941,JP-A-11-185959 and JP-A-11-144872. However, theinvention is not limited by these. Additionally, dotted lines in thefollowing chemical formulae represent coordination bonds.

[0146] Next, the host material is described below. The compounds of theinvention represented by the general formula (I) generally have anabsorption in a green region, and hence, in order to emit light with ahigh efficiency by energy transfer from the host material, it isnecessary to match the light-emitting spectrum of the host material withthe absorption spectrum. The host material to be used in the inventiongenerally emits a green light in the case where the compound representedby the general formula (I) is not contained. The host material ispreferably a triarylamine compound, a styryl compound, an aromatic fusedmulti-ring compound or an organometalic complex, more preferably a metalcomplex of a 8-quinolinol derivative, particularly preferablyAlq(tris(8-hydroxyquinolinato)aluminum.

[0147] Next, the EL element containing the compound of the invention isdescribed below. Although methods for forming the organic layer of theEL element containing the compound of the general formula represented bythe general formula (I) is not particularly limited, there may beemployed a vacuum deposition method by resistance heating, an electronbeam method, a sputtering method, a molecule-laminating method, acoating method, an inkjet method, a printing method or a transfermethod. In view of properties and production aspects, a vacuumdeposition method by resistance heating and a coating method arepreferred.

[0148] The light-emitting element of the invention is an element whereina light-emitting layer or a plurality of organic compound thin layersincluding the light-emitting layer are formed between a pair ofelectrodes of an anode and a cathode. The element may contain a holeinjecting layer, a hole transporting layer, an electron injecting layer,an electron transporting layer and a protective layer in addition to thelight-emitting layer. Each of these layers may have functions of otherlayers. Various materials may be used for forming respective layers.

[0149] The anode functions to feed holes to the hole injecting layer,the hole transporting layer and the light-emitting layer, and a metal,an alloy, a metal oxide, an electrically conductive compound or amixture thereof may be used for it, with materials having a workfunction of 4 eV or more being preferred. Specific examples thereofinclude electrically conductive metal oxides such as tin oxide, zincoxide, indium oxide and indium tin oxide (ITO), metals such as gold,silver, chromium and nickel, mixtures or laminates of these metals andthe electrically conductive metal oxides, inorganic electricallyconductive materials such as copper iodide and copper sulfide, organicelectrically conductive materials such as polyaniline, polythiophene andpolypyrrole, and laminates of these materials and ITO, with electricallyconductive metal oxides being preferred. Particularly, in view ofproductivity, high conductivity and transparency, ITO is preferred. Thethickness of the anode may properly be selected, but is preferably 10 nmto 5 μm, more preferably 50 nm to 1 μm, still more preferably 100 nm to500 nm.

[0150] As the anode, an anode obtained by forming a layer of theabove-described material on a substrate of soda-lime glass, alkali-freeglass or transparent resin. In the case of using glass, it is preferredto use alkali-free glass so as to reduce the amount of ions dissolvedfrom the glass. Also, in the case of using soda-lime glass, it ispreferred to use soda-lime glass having provided thereon a barrier coatof silica or the like. The thickness of the substrate is notparticularly limited as long as it is enough to maintain mechanicalstrength and, in the case of using glass, the thickness is usually 0.2mm or more, preferably 0.7 mm or more.

[0151] Various methods may be employed for preparing the anode dependingupon the kind of the material and, in the case of, for example, ITO, themembrane is formed by a method such as an electron beam method, asputtering method, a vacuum deposition method by resistance heating, achemical reaction method (e.g., sol-gel method) or a method of coating adispersion of ITO, or like method.

[0152] Washing or other treatment of the anode permits to reduce thedriving voltage or enhance light-emitting efficiency. In the case of,for example, ITO, UV-ozone treatment or plasma treatment is effective.

[0153] The cathode functions to feed electron to the electron injectinglayer, the electron transporting layer and the light-emitting layer, andis selected by considering adhesion properties to a layer adjacentthereto such as the electron injecting layer, the electron transportinglayer and the light-emitting layer, ionization potential and stability.As materials for the cathode, a metal, an alloy, a metal oxide, anelectrically conductive compound and the mixture thereof may be used.Specific examples thereof include an alkali metal (e.g., Li, Na, K orCS) or the fluoride or oxide thereof, an alkaline earth metal (e.g., Mgor Ca) or the fluoride or oxide thereof, gold, silver, lead, aluminum,sodium-potassium alloy or the mixture metal thereof, lithium-aluminumalloy or the mixture metal thereof, magnesium-silver alloy or themixture metal thereof, and a rare earth metal such as indium orytterbium. More preferred are those which have a work function of 4 eVor less, with aluminum, lithium-alluminum alloy or the mixture metalthereof, and magnesium-silver alloy or the mixture metal thereof beingmore preferred. The thickness of the cathode may properly be selected,and is preferably in the range of 10 nm to 5μ, more preferably 50 nm to1 μm, still more preferably 100 nm to 1 μm.

[0154] The cathode may be prepared by a method such as an electron beammethod, a sputtering method, a vacuum deposition method by resistanceheating or a coating method, and the metal may be vacuum-deposited as asingle body, or two or more metals may be vacuum-deposited at the sametime. Further, it is possible to vacuum-deposit a plurality of metals toform an alloy electrode or, alternatively, a previously prepared alloymay be vacuum-deposited.

[0155] As to the sheet resistances of the anode and the cathode, smallerresistances are preferred, with several hundreds Ω or less beingpreferred.

[0156] The material of the light-emitting layer contains at least onecompound of the invention represented by the general formula (I), andmay contain two or more of the compounds represented by the generalformula (I). Also, other light-emitting materials than the compoundsrepresented by the general formula (I) may be used together with thelight-emitting material of the invention, and any compound may be usedthat can form a layer which, upon application of an electric field,permits to inject holes from the anode or from the hole injecting layeror the hole transporting layer and permits to inject electrons from thecathode or from the electron injecting layer or the electrontransporting layer, which functions to move the injected charge, andwhich provides the site where the hole and the electron recombines topermit emission of light. As the compounds to be used in thelight-emitting layer, either of those which emit a light from excitedsinglet and those which emit a light from excited triplet may be used.For example, there may be illustrated benzoxazole, benzimidazole,benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene,tetraphenylbutadiene, naphthalimide, coumarin, perylene, perynone,oxadiazole, aldazine, pyralizine, cyclopentadiene, bisstyrylanthracene,quinacridone, pyrrolipyridine, thiadiazolopyridine, styrylamine,aromatic dimethylidyne compound, metal complexes of 8-quinolinol,various metal complexes represented by organometallic complexes and rareearth metal complexes, the derivatives of the above-described compounds,and polymers such as polythiophene, polyphenylene andpolyphenylenevinylene as well as the compounds of the invention. Thethickness of the light-emitting layer is not particularly limited, butis preferably in the range of from 1 nm to 5 μm, more preferably from 10nm to 500 nm.

[0157] Methods for forming the light-emitting layer are not particularlylimited, and there may be employed a vacuum-depositing method byresistance heating, an electron beam method, a sputtering method, amolecule-laminating method, a coating method( e.g., a spin-coatingmethod, a cast coating method or a dip-coating method), an LB method, aninkjet method, a printing method and a transfer method, with avacuum-depositing method by resistance heating and a coating methodbeing preferred.

[0158] As the materials for the hole injecting layer and the holetransporting layer, any one may be used that has one of the function toinject holes from the anode, the function of transporting holes, and thefunction of blocking electrons injected from the cathode. Specificexamples thereof include carbazole, imidazole, triazole, oxazole,oxadiazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine,arylamine, amino-substituted chalcone, styrylanthracene, fluorenone,hydrazone, stilbene, silazane, aromatic tertiary amine compound,styrylamine, aromaticdimethylidyne compounds, porphyrin-based compound,polysilane-based compound, poly(N-vinylcarbazole), aniline-basedcopolymer, electrically conductive high molecular oligomers and polymerssuch as thiophene oligomers and polymers and polythiophene, carbon filmand derivatives of the above-described compounds. The thickness of thehole injecting layer and the hole transporting layer is not particularlylimited depending upon the kind of the material, but is preferably inthe range of from 1 nm to 5 μm, more preferably from 5 nm to 1 μm, stillmore preferably from 10 nm to 500 nm. The hole injecting layer and thehole transporting layer may be a single-layer structure comprising one,two or more of the materials described above, or may be a multi-layerstructure composed of a plurality of layers of the same formulation ordifferent formulations.

[0159] As a method for forming the hole injecting layer and the holetransporting layer, there may be employed a vacuum deposition method, anLB method, an ink jet method, a printing method, a transfer method, acoating method of dissolving or dispersing the aforementioned holeinjecting material or the hole transporting material in a solvent (e.g.,a spin-coating method, a cast-coating method or a dip-coating method).With the coating method, the materials may be dissolved or dispersedtogether with a resin component, and examples of such resin componentsinclude polyvinyl chloride, polycarbonate, polystyrene,polymethylmethacrylate, polyester, polysulfone, polyphenylene oxide,polybutadiene, poly(N-vinylcarbazole), hydrocarbon resin, ketone resin,phenoxy resin, polyamide, ethyl cellulose, vinyl acetate, ABS resin,polyurethane, melamine resin, unsaturated polyester resin, alkyd resin,epoxy resin and silicone resin.

[0160] Also, the thickness of the organic membrane to be used in theinvention which exists between the light-emitting alyer and the cathodeis not particularly limited, and is preferably 0.1 nm to 100 nm, morepreferably 2 nm to 50 nm, still more preferably 5 nm to 40 nm.

[0161] Methods for forming the organic membrane are not particularlylimited, and there may be employed a vacuum deposition method, an LBmethod, an ink jet method, a printing method, a transfer method, acoating method of dissolving or dispersing the aforementioned holeinjecting material or the hole transporting material in a solvent (e.g.,a spin-coating method, a cast-coating method or a dip-coating method).

[0162] As materials for the electron injecting layer and the electrontransporting layer, any of those which exert one of the function ofinjecting electrons from the cathode, the function of transportingelectrons and the function of blocking holes injected from the anode maybe used with no limitations. Specific examples thereof include triazole,triazine, oxazole, oxadiazole, fluorenone, anthraquinodimethane,anthrone, diphenylquinone, tiopyran dioxide, carbodiimide,fluorenylidenemethane, distyrylpyrazine, aromatic tetracarboxylic acidanhydrides such as naphthaleneperylene, phthalocyanine, various metalcomplexes exemplified by metal complexes of 8-quinolinol derivatives ormetal phthalocyanine, or metal complexes containing as a loigandbenzoxazole or benzothiazole, and derivatives of the above-describedcompounds. The thickness of the electron injecting layer and theelectron transporting layer is not particularly limited, but ispreferably in the range of from 1 nm to 5 μm, more preferably from 5 nmto 1 μm, still more preferably from 10 nm to 500 nm. The electroninjecting layer and the electron transporting layer may be asingle-layer structure comprising one, two or more of the materialsdescribed above, or may be a multi-layer structure composed of aplurality of layers of the same formulation or different formulations.

[0163] As a method for forming the electron injecting layer and theelectron transporting layer, there may be employed a vacuum depositionmethod, an LB method, an ink jet method, a printing method, a transfermethod, a coating method of dissolving or dispersing the aforementionedelectron injecting material or the electron transporting material in asolvent (e.g., a spin-coating method, a cast-coating method or adip-coating method). With the coating method, the materials may bedissolved or dispersed together with a resin component and, as suchresin components, those illustrated with respect to the hole injectingand transporting layer may be used.

[0164] As the material for the protective layer, any of those whichfunction to prevent invasion of element deterioration-acceleratingsubstances such as moisture and oxygen may be used with no limitations.Specific examples thereof include metals such as In, Sn, Pb, Au, Cu, Ag,Al, Ti and Ni, metal oxides such as MgO, SiO, SiO₂, Al₂O₃, GeO, NiO,CaO, BaO, Fe₂O₃, Y₂O₃ and TiO₂, metal fluorides such as MgF₂, LiF, YalF₃and CaF₂, polyethylene, polypropylene, polymethyl methacrylate,polyimide, polyurea, polytetrafluoroethylene,polychlorotrifluoroethylene, polydichlorodifluoroethylene, copolymerbetween chlorotrifluoroethylene and dichlorodifluoroethylene, copolymerobtained by copolymerizing a monomer mixture containingtetrafluoroethylene and at least one comonomer, fluorine-containingcopolymer containing a cyclic structure in the copolymer main chain, awater-absorbing substance having a water absorption of 1% or more and amoisture-resistant substance having a water absorption of 0.1% or less.

[0165] Methods for forming the protective layer are not particularlylimited, and there may be employed, for example, a vacuum depositionmethod, a sputtering method, a reactive sputtering method, an MBE(molecular beam epitaxy) method, a cluster ion beam method, anion-plating method, a plasma polymerization method(high-frequency-excited ion plating method), a plasma CVD method, alaser CVD method, a heat CVD method, a gas source CVD method, a coatingmethod, an ink jet method, a printing method and a transfer method.

EXAMPLES

[0166] The invention is now described by reference to Examples of theinvention and Comparative Examples which, however, do not limit theinvention in any way.

Comparative Example 1

[0167] A transparent supporting substrate (made by Tokyo Sanyo ShinkuK.K.) comprising a 25 mm×25 mm×0.7 mm glass substrate having formedthereon a 150-nm thick ITO was used as a substrate. After etching andwashing this transparent supporting substrate, the substrate was placedin a vacuum deposition apparatus, and TPD(N,N′-diphenyl-N,N′-di(m-tolyl)-benzidine) was vacuum deposited in athickness of 40 nm, and a compound of the invention (D-1) and Alq (tris(8-hydroxyquinolinato) aluminum) were vacuum co-deposited at vacuumdeposition rates of 0.004 nm/sec and 0.4 nm/sec, respectively in avacuum of 10⁻³ to 10⁻⁴ Pa under the condition of room temperature insubstrate temperature to form a 60-nm thick layer. Further, a patternedmask (for attaining light-emitting area of 4 mm×5 mm) was mounted on theorganic thin film and, after vacuum co-depositing magnesium and silver(Mg:Ag=10:1) in a thickness of 250 nm, silver was vacuum deposited in athickness of 250 nm, followed by sealing the element to prepare an ELelement (Element No.101).

Comparative Example 2

[0168] After etching and washing the ITO substrate in the same manner asin Comparative Example 1, TPD was vacuum-deposited in a thickness ofabout 40 nm. Then, the compound of the invention (D-1) and Alq(tris(8-hydroxyquinolinato)aluminum) were vacuum co-deposited at vacuumdeposition rates of 0.004 nm/sec and 0.4 nm/sec, respectively to form a40-nm thick layer. Further, as a third layer, Alq alone was vacuumdeposited in a thickness of 20 nm, then a cathode was vacuum depositedin the same manner as in Comparative Example 1, followed by sealing theelement to prepare an EL element (Element No. 102).

Example 1

[0169] After etching and washing the ITO substrate in the same manner asin Comparative Example 1, TPD was vacuum-deposited in a thickness ofabout 40 nm. Then, the compound of the invention (D-1) and Alq(tris(8-hydroxyquinolinato)aluminum) were vacuum co-deposited at vacuumdeposition rates of 0.004 nm/sec and 0.4 nm/sec, respectively to form a40-nm thick layer. Further, as a third layer, the compound of theinvention (E-16) alone was vacuum deposited in a thickness of 20 nm,then a cathode was vacuum deposited in the same manner as in ComparativeExample 1, followed by sealing the element to prepare an EL element(Element No. 103). Further, similar elements (Element No. 104 to 106)were prepared by changing the light-emitting material to those describedin Table 1.

[0170] Then, each of the elements was evaluated in the following manner.Results thus obtained are shown in Table 1.

Maximum Luminance and Wavelength of Emitted Light

[0171] A constant direct current was applied to each of the EL elementsusing a source measure unit 2400 made by Toyo Tekunika on the organicmembrane to render the elements of Comparative Examples and Examples ofthe invention emit a light. The luminance of each of the thus-emittedlights was measured by means of a luminance meter, BM-8, made by TopukonK. K. to compare. The wavelength of each of the emitted lights wasmeasured by means of a spectrum analyzer (PMA-11; Hamamatsu PhotonicsCo., Ltd.).

Temperature Dependence of Light-Emitting Period of Emitted Light Pulse(Width of Emitted Light Pulse)

[0172] The temperature of the element was adjusted to 15° C., and 10-nsintermittent pulse driving was imparted to the element at 10V to measurethe light-emitting period per pulse. Then, the temperature of theelement was raised to 55° C., and the light-emitting period per pulsewas similarly measured. The temperature dependence of the light-emittingperiod of emitted light pulse (width of emitted light pulse) wasevaluated in terms of the values calculated according to the followingformula. The nearer to 1 the value is, the smaller is the temperaturedependence.

Temperature dependence=Light-emitting period at 15° C./Light-emittingperiod at 55° C. TABLE 1 Temperature Dependence Light- MaximumWavelength of of Pulse Width Element emitting Luminance Emitted Light ofEmitted No. Material (cd/m²) Elmax (nm) Light 101 D-1  2000 616 0.83 102D-1  2420 614 0.82 103 D-1  4050 610 0.93 104 D-22 3500 658 0.92 105D-27 6100 603 0.93 106 D-34 3000 630 0.91

Compounds Used in Comparative Example 1, Comparjative Example 2 andExample 1 are Shown Below.

[0173] Additionally, the values of ionization potential (IP) given beloware obtained by a photoelectric spectral apparatus (AC-1; made by RikenKeiki), cyclic voltammetry, and from literature (unit: eV).

[0174] As is apparent from the results in Table 1, the elements of theinvention can emit a light with a high luminance and a high efficiency,and show a temperature dependence of the pulse width of emitted lightnear to 1, thus being excellent.

Example 2

[0175] After etching and washing the ITO substrate in the same manner asin Comparative Example 2, TPD was vacuum-deposited in a thickness ofabout 40 nm. Then, the compound of the invention (D-1) and Alq(tris(8-hydroxyquinolinato)aluminum) were vacuum co-deposited at vacuumdeposition rates of 0.004 nm/sec and 0.4 nm/sec, respectively to form a40-nm thick layer. Further, as a third layer, each of the compoundsdescribed in Table 2 alone was vacuum deposited in a thickness of 5 nm,then, as a fourth layer, Alq was vacuum deposited thereon in a thicknessof 15 nm. Subsequently, a cathode was vacuum deposited in the samemanner as in Example 1, followed by sealing the element to prepare ELelements (Element Nos. 201 to 207). TABLE 2 Compound of TemperatureDependence of Pulse Element No. 3^(rd) Layer Width of Emitted Light 201E-16  0.93 202 E-4  0.90 203 E-1  0.91 204 E-67  0.85 205 E-111 0.87 206E-117 0.89 207 E-125 0.87

[0176] Compounds used in Example 2 are shown below.

[0177] Results obtained by measuring temperature dependence of pulsewidth in the same manner as in Example 1 are shown in Table 2. It can beconfirmed from the results that, in comparison with Comparative Example2 (Element No. 102), the elements of the invention have a lesstemperature dependence of the pulse width of emitted light.Additionally, red purity of the elements No. 101 to 106 and 201 to 207were good.

[0178] While the invention has been described in detail and by referenceto specific embodiments, it is apparent to those skilled in the art tomake various alterations and modifications without departing from thespirit and the scope of the invention.

[0179] This application is based on Japanese Patent Application No.2001-101027 filed on 30, Mar. 2001, and the contents are incorporatedherein as a reference.

Industrial Applicability

[0180] The light-emitting element of the invention has a smalltemperature dependence of the pulse width of emitted light upon pulsedriving, and are excellent in red purity, light-emitting efficiency anddurability. Hence, the light-emitting element of the invention maysuitably be used in the field of backlight, flat panel display,illuminating light sources, display elements, electrophotography,organic semiconductor lasers, recording light sources, exposing lightsources, reading light sources, signs, signboards and opticalcommunication devices.

What is claimed is:
 1. A light-emitting element, which comprises asubstrate having provided thereon a pair of opposed electrodes betweenwhich are provided a light-emitting layer containing at least onelight-emitting material selected from the compounds represented by thefollowing general formula (I) and a host material, and which comprisesan organic membrane having a larger ionization potential than that ofthe host material between the light-emitting layer and a cathode, theorganic membrane being in contact with the light-emitting layer:

wherein R¹, R², R³, R⁴ and R⁵ may be the same or different from eachother and each represents a hydrogen atom or a substituent, X representsan oxygen atom, a sulfur atom or N—R^(Y1), R^(Y1) represents a hydrogenatom or a substituent, L represents a linking group comprising aconjugated bond, R^(X) and R^(Y) may be the same or different from eachother and each represents a hydrogen atom or a substituent, with atleast one of them being an electron-withdrawing group.
 2. Thelight-emitting element of claim 1,wherein a difference in ionizationpotential between the organic membrane and the host material in thelight-emitting layer is 0.01 eV to 2 eV.
 3. The light-emitting elementof claim 1 or 2, wherein an ionization potential of the organic membraneis more than 5.7 eV and not more than 7.0 eV.
 4. The light-emittingelement of one of claims 1 to 3, wherein the organic membrane comprisesat least one compound selected from the compounds represented by thegeneral formulae

wherein, in the general formula (V), R⁵⁵ and R⁵⁶ may be the same ordifferent from each other and each represents an alkyl group, an arylgroup or a hetero ring group, X⁵ represents an oxygen atom, a sulfuratom or N—R^(Y5), and R^(Y5) represents a hydrogen atom or a substituentand, in the general formula (VI), A represents a hetero ring groupcontaining two or more hetero atoms, with the hetero ring groupsrepresented by A being optionally the same or different from each other,m⁶ represents an integer of 2 or more, and L⁶ represents a linking groupand, in the general formula (VII), R⁷¹ represents a substituent, R⁷²represents a hydrogen atom, an aliphatic group, an aryl group or anaromatic hetero ring group, M represents a metal atom, n⁷ represents aninteger of 0 to 6 and m⁷ represents 2 or 3, with the proviso that, whenm⁷=3, then n⁷≠0 and, in the general formula (VIII), X⁸¹ represents anitrogen atom or C—R⁸¹, X⁸² represents an oxygen atom, a sulfur atom orN—R^(Y8), R⁸¹, R⁸², R⁸³ and R^(Y8) may be the same or different fromeach other and each represents a hydrogen atom or a substituent, withR⁸¹ and R⁸² being optionally connected to each other to form a ring, R⁹⁴represents a hydrogen atom, an alkyl group, an aryl group or an aromatichetero ring group, M represents a metal atom, n8 represents an integerof 0 to 4, and m⁸ represents 2 or 3 and, in the general formula (IX),R⁹¹ represents a substituent, with a plurality of R⁹¹s optionally beingconnected to each other to form a fused ring, R⁹² to R⁹⁴ may be the sameor different from each other and each represents a hydrogen atom or asubstituent, and m⁹ represents an integer of 0 to 5 and, in the generalformula (X), R¹⁰¹ and R¹⁰² may be the same or different from each otherand each represents a hydrogen atom or a substituent, R¹⁰³ to R¹⁰⁶ maybe the same or different from each other and each represents asubstituent, L¹⁰ represents a linking group, and m¹⁰, n¹⁰, p¹⁰ and q¹⁰may be the same or different from each other and each represents aninteger of 0 to 5 and, in the general formula (XI), Ar¹¹¹ represents atrivalent arylene group, Ar¹¹² to Ar¹¹⁴ may be the same or differentfrom each other and each represents an aryl group.
 5. The light-emittingelement of one of claims 1 to 4, wherein the compound represented by thegeneral formula (I) is a compound represented by the following generalformula (II):

wherein R¹, R², R³, R⁴ and R⁵ may be the same or different from eachother and each represents a hydrogen atom or a substituent, X representsan oxygen atom, a sulfur atom or N—R^(Y1), R^(Y1) represents a hydrogenatom or a substituent, Z² represents atoms necessary for forming 5- or6-membered ring, L₂₁ and L₂₂ may be the same or different from eachother and each represents a methine group, a substituted methine groupor a nitrogen atom, n represents an integer of 0 to 3, and Ar representsan arylene group or a divalent aromatic hetero ring group.
 6. Thelight-emitting element of claim 5, wherein the compound represented bythe general formula (II) is a compound represented by the followinggeneral formula (III):

wherein R¹, R², R³, R⁴, R⁵, R³¹, R³², R³³ and R³⁴ may be the same ordifferent from each other and each represents a hydrogen atom or asubstituent, Z³ represents atoms necessary for forming 5- or 6-memberedring, L₂₁ and L₂₂ may be the same or different from each other and eachrepresents a methine group, a substituted methine group or a nitrogenatom, and n represents an integer of 0 to
 3. 7. The light-emittingelement of claim 6, wherein the compound represented by the generalformula (III) is a compound represented by the following general formula(IV):

wherein R¹, R², R³, R⁴, R⁵, R³¹, R³², R³³, R³⁴, R⁴¹, R⁴², R⁴³ and R⁴⁴may be the same or different from each other and each represents ahydrogen atom or a substituent, and R^(A1) and R^(A2) may be the same ordifferent from each other and each represents a hydrogen atom or asubstituent and, when possible, R^(A1) and R^(A2) maybe connected toeach other and further to other substituent to form a ring.
 8. Thelight-emitting element of one of claims 1 to 7, wherein the hostmaterial is an aluminum quinoline derivative.
 9. The light-emittingelement of one of claims 1 to 8, wherein a content of the at least onecompound selected from the compounds represented by the general formulae(I) to (IV) in the light-emitting layer is 0.01% by weight to 50% byweight.
 10. The light-emitting element of one of claims 4 to 9, whereina content of the at least one compound selected from the compoundsrepresented by the general formulae (V) to (XI) in the organic membraneis 50% by weight to 100% by weight.